1. Technical Field
The present invention relates generally to a motion detection system, and more particularly, to a non-contact, movement-measurement and position-tracking device and to a method of applying the device on long, non-textured or regularly textured metal objects at an elevated temperature.
2. Description of the Related Art
Vision systems have been used to provide non-contact movement measurement and position tracking for small objects, such as a baseball or a pin-pong ball, and for textured long objects, such as a cloth web with printed pattern. In these applications, specific patterns (color or optical geometry) are used to identify the position of the object or the movement (both in quantity and direction) of the object. Such specific patterns must be unique in a specific area of the field of view of the vision systems.
However, for a long, non-textured (or regularly textured) object, such as a long steel bar or a long steel sheet/strip, vision systems have no unique patterns to track. The patterns on a “regularly textured” object cannot provide the uniqueness for the purpose of identifying (tracking) the same point on the object.
In a steel mill or a forging shop, it is often necessary to track a long metal object, such as a hot-rolled steel rod, with accuracy. One such application is to measure the feed length of a steel rod as such rod is at an elevated temperature when the rod is fed into a forging press and cut/sheared into short segments of a specific length. While painted features may be added to the object in some applications, it is impossible to do so on a hot steel surface because no non-destructive marking material exists for hot surfaces.
One of the present arts is to use a contact wheel or a contact slide. Such device has a contact head that is engaged with the hot metal rod and move along with the hot metal rod. There is a measurement device, such as a resolver, an encoder, a linear scale, or the like integrated in the device. There are drawbacks in this approach. The contact head may wear and thus induce significant deviations in accuracy over time. The contacting device needs intensive cooling to prevent overheating. The contacting device needs perfect alignment to the motion of the hot metal rod in order to provide accurate measurements. The contacting device occupies valuable space in the hot metal working equipment. Installation of the contacting device requires a significant period of down time of the hot metal working equipment.
Another approach is dead reckoning. In this approach, the starting end of the metal rod is detected while the metal rod is still at room temperature. As the metal rod moves through the heating elements, a motion estimator, either based on time (and assumed moving speed) or based on the number of strokes (and the nominal feed length per stroke), is used to estimate how much the metal rod has moved. This approach is not accurate. There could be very significant accumulated errors in the measurement due to variation in moving speed and feed length.
The present invention is to provide a means and a method to measure and track the motion of a long, non-textured metal object at an elevated temperature that is non-contact and accurate.